In many facilities, the normal movement of individuals or equipment across floors can generate electrostatic charges. The conducting or sparking of these electrostatic charges can cause serious problems with equipment and products. Electrostatic charges can also create malfunctions in the internal circuitry of electrical equipment being manufactured or being used in particular facilities. Computer equipment, for example, is prone to malfunctions caused by electrostatic charges. When manufacturing electrical components, especially integrated circuit chips, the avoidance of electrostatic charge is critical because such components are extremely charge sensitive.
In facilities using combustible or explosive materials, sparking can result in dangerous explosions or fires. In hospitals, sparking near an oxygen source can increase the chances of fire. Sparking can also affect charge sensitive electrical equipment being used in care units or operating rooms. Such sparking can even affect the physical condition of a patient being operated on.
Because of the problems and dangers associated with electrostatic charges, various standards have been set requiring-facility floors to meet minimum resistance values and to dissipate electrostatic charges at a minimum rate. For example, the NFPA (National Fire Protection Association) 99 standard requires that the resistance of a floor be more than an average of 25,000 ohms. When measuring the resistance of a floor according to the NFPA 99 standard, a five pound metal weight is placed on the floor, and the resistance from the weight to ground is measured. Several measurements at different points on the floor should be made, and the measurements are averaged to get a value for the floor resistance.
For military purposes, the federal government classifies flooring structures as being conductive, anti-static or dissipative. A flooring structure is considered anti-static if it has a resistance of 10.sup.9 to 10.sup.14 ohms per square. A flooring structure with this resistance does not create any static electricity but discharges static charges at a very slow rate. Materials that are insulators have resistances of higher than 10.sup.14 ohms per square. Flooring structures with resistances between 10.sup.5 and 10.sup.9 ohms per square are considered dissipative. Dissipative flooring structures do not create any electrostatic charges and discharge any existing electrostatic charges at a quick rate. Conductive flooring structures have resistances of less than 10.sup.5 ohms per square and discharge electrostatic electricity at a very quick rate, but this rate might be so fast as to create a surge capable of damaging electrical components. Anti-static floor structures are effective in some applications, but electrostatic dissipative or discharge flooring structures are useful in most applications.
To eliminate problems associated with electrostatic charges, and to meet the established resistance standards, various floor composition designs have been attempted to prevent the conduction of electrostatic charges and dissipate these electrostatic charges through ground. Although insulative materials prevent the conduction of electrostatic charges, they have been found to be undesirable because they may allow electrostatic charges created by frictional effects to accumulate. See U.S. Pat. No. 2,325,414 by McChesney et al. Surface materials of a hard metallic nature are highly conductive. As discussed above, conductive materials discharge electrostatic charges at a rapid rate, but the rate of discharge might be too rapid, creating a surge. These hard metallic materials are also undesirable since they could produce sparks if struck by another metal object. See U.S. Pat. No. 3,121,825 by Abegg et al. Semi-conductive floor materials were developed to overcome the problems associated with insulating and conducting materials. These semiconductive floor-materials, for example semiconducting rubber or thermoplastic floor tiles containing flakes of conductive material, were designed to have a resistance value such that the material does not accumulate electrostatic charges and discharges electrostatic charges at a sufficient rate.
The principal problem with semiconductive floor materials is that it is difficult to achieve an even distribution of the insulating and conducting material used in fabricating the semiconductive material. This can result in an uneven distribution of electric charges, and varying degrees of electrostatic charge dissipation. To eliminate these problems, conductive screens or meshes have been imbedded in the semiconductive material and attached to a ground terminal. The concept for this type of flooring is that the electrostatic charges travel only short distances in the semiconductive material before they pass through the highly conductive mesh or screen to ground, and since this screen or mesh is uniformly imbedded throughout the semiconductive material, the discharge of the electrostatic charges is uniform throughout.
However, there are several reasons why even these flooring materials fail to adequately discharge the electrostatic charges. Over a period of time, the conductivity and resistance of the semiconductive material, the conductive screen or mesh, and any materials used to affix the layers together or to affix the flooring to ground tend to change. Furthermore, moisture, which is a common occurrence in flooring, not only damages these floors but also causes them to become more conductive than designed.
From the foregoing, it can be seen that a need exists for a flooring structure that dissipates electrostatic charges within adopted standards, and has a resistance that can be monitored and changed to insure that the flooring structure has the desired resistivity. Furthermore, a need exists for an electrostatic discharge controlling flooring structure that is not affected by the first occurrences of moisture, and that contains a monitor for sensing the presence of such moisture. A further need exists for a flooring system made up of multiple flooring structures insulated from each other so that each flooring structure of the flooring system can have a different resistance.